Manufacture of steel



Patented June 26, '1951;

UNITED STATES PATENT OFFICE NoDrawing; Application May.18`, 19150', Serialo. 162,811- Iii-.Belgium Nvllir5, 1941V section 1. ifubrie Law 690,. Augusta-,.1946 Patent expires November 5, 1961 9..Gla'ims; 1 l

This invention relates tij-manufacture of steel;

andl it comprisesamethod particularly'applicable toi the'- open hearth process wherein aY steelfur'- 11a-cells charged with metallic steel-making irrgredients;l the charge including assubstantially the sole carbu-rizing, deoxidizingQdegasifyifr/ig component a carbon-impregnated lime product, followedby converting the charge in the furnace to steel said lime pro'ductbeing one produceisll by calcining.` rock limestone, coarsely`4 crushing' the resultinglimer treating the limeV in lli-mp format temperatureso` the' order of 250 C. with arr eri-'- cess of. al moltenrbitminous materiali substantially uniformly to.r impregnate the pores of the lumps with'V saidbituminoiis material; and drain-- ing on the excessi bituminous material to obtain a product .in lumps` forms havingthe structure of the original limestone With'` from about' 25 to 35 p'er cent by Weight of saidlbituminousmaterial substantiallyY uniformly distributed@ throughout its poresin ar highly dispersedrstate;v all asA more fullyhereinafter set fortlr and". as'V claimed. Y This application'. is av continuationein-Hpart o'f my; copending application` Serial` No.- 732,375', filed-March 4,1947, now abandoned.v In'thepmf ent application my' process is described-inf general terms and illustrated with a specic example While inthe present application the descriptionlis amplified by the `addition of two additional' spe"V cilcexamples andby deiining` the invention. more specifically. K

In: the conventional open hearth processA of makingsteel the chargeusually consists ofse'rap iron; pig iron and/or cast iron and slageforming components. The pig iron and/or scrap iron in the charge serves as a carburizing and deoxidiz`= ing agent. In many cases it would be advan-V tageous to eliminate the pig and/or cast iron from the charge but prior to the present invention no suitable carburizingand# deoxidizingagent has been discovered which Would be entirely. suitable as a replacement.

I- have discovered that if rock limestone'isfc'al-v cined, coarsely crushed and then treated. With a molten bituminous material under conditions producing substantially uniform impregnation with bitumen of the pores'o'f the pieces of. lime down to their'deepest regions; this' product, which retains the original structure of' the limestone and which has considerable mechanical strength, can be incorporated in a steel-making charge substantially' as the 'sole vcarburizing, deoxidizingdegasifying componentl A` steel is obtained Whichis very pure' and which" possesses rriechan` ical properties- Whichareextremely adi/anta` I" have ffourid that this result cannot be progdiced' the lime product is impregnated only supriallf oi if` the lime is plveri'z'ed' andmade into briquetts rising trie same `airrcur'it of 'bituiios' materiales abiide'r. Bri('i'.iie'ttes4 of this typ' disintegrate d'rir'rg the heating" andthe bitumino u's material tli biis Without ectig any substantial `cariniriizin"A effect.' The saine. is true ifitire' bitummcusniateriai ispresnt merely as' a" coating? on thelimeLv particles. When'4 new imp regna'ted lime precinct is employed; in contrast, the carbon' isgraduarlly' andcntnv ou'sly released' from thejpp'res or the lime" partiI-4 cieseduringf ure i entireheat anu thus precoces the" redui'red carbi'irizi'nig,` deoXidizinLgLdegasify; ing el'ect.' v Y I`-have discovered three different irie'thodsby means of Whiclrthe Vlime particles' can"A befs'atis factoril'y impregnated." InJ the first two" oftthese methods* a; dirfe'r'ertiar a-ir" pressure iserpyed to drive: the moit'e'n bituminous material into the: pores: Thus the'- l-ime productiesubjected to reduced pre's'suifes='justbefore`Y or' wl'iiie itis beingcontacted melt'enl bitumen; Ifhisre movesl-tlfef air from thel pores" and their Wherr the vacuiinri's- 'releasedA or superatmo'sphericj pres sure is appiiiit the differentiar pressure thereby prodi-iced# forces'-` tlierl'i'tfmerr intoL the pores: An equivalent result is produced by the usefor siip`er= atmdse'ric priess'ui'es'al'orie diiifingftlre impregnatin step; the ess/lires tending''to' forceftlie Inolteir bituiier to'' theporfe's.- Itsonlynec-w essa-ry tof establishffa pressureon the bitumen"y which; is higher thanl the' pressu theaporesfofithef lime 1'J'article's. SLi-fprisi have also?` rounds that satisfactoryv impregnamon canI be achieved byheating thelimaproduct with an excess'otmolten bitumen over'an'open llame,- ior exampl'e by; heating-z the lime'v with molten bitumen im a vesseli directly? heated with.V an". open flame for a Deriodi'offrom' about' 3ft@ 4'* hours with ther' hotx gases contactingI the 1 materiali under treatment.

The ealcinedl'rockf. limestone which isf irnpreg-V natedi my processv should. be'v coarselyv crushed so thatnoparticlesexceed aboutl l0i mani and finesl shouldiube'eliminated before the impregnation st'epf.- Unlessatreshly calcinecl` productis and the like are examples of suitable bituminous materials.

The impregnating step of my process is conveniently conducted in an autoclave, at least when a differential pressure is relied upon to produce the desired degree of impregnation. The crushed lime product, vafter being subjected to a drying operation if necessary, is charged into the autoclave. In my preferred process the autoclave is then heated and evacuated to remove air from the pores of the lime. The bituminous material is heated in a separate container to a temperature of the order of 250 C.,

and, after the occluded gases have been removed from the lime, the liquid bituminous material is injected into the autoclave, preferably under pressure. The bituminous material evolves gases and, if the autoclave is kept closed and its temperature maintained at approximately 250 C., the pressure inside soon builds up to superat- 'mospheric pressures. This tends to force the Abituminous material into the pores of the lime. After heating for several hours the bituminous material is drained from the impregnated lime product and after cooling the latter is then ready 'to be used in my steel making process.

It is possible to omit the initial evacuating step of the process described in the preceding paragraph and a substantially equal degree of impregnation can be obtained if the autoclave is heated when closed for a slightly longer period. During thisheating period the pressure in the autoclave may build up to l kilograms per square centimeter or higher depending upon the bituminous material employed. Air or other gases may be passed into the autoclave to produce a superatmospheric pressure if desired.

If an autoclave is not available I have found it possible to obtain a satisfactory impregnation of the lime merely by prolonged heating of the crushed lime at a temperature of approximately 250 C. in contact with a large excess of molten Vbituminous material in an, open vessel heated by an open flame. The occluded gases in the pores of the lime expand under thesev conditions and .gradually escape from the charge While the molten .bitumen is simultaneously absorbed into the pores.

Allof the three impregnating processes der scribed, when conducted properly, produce inherently av lime product the pores of which are impregnated substantially uniformly and to their `deepest regions with bitumen in a highly dispersed state and in quantity amounting to from about 25 to 35 per cent by weight. The particles ofthis product may be distilled off by heating of the impregnated product to remove volatiles. In this case the remaining bitumen is largely in the form of carbon. The nal impregnated product is highly stable. It is substantially impervious to moisture and it does not slake or disintegrate under ordinary conditions. It can be shipped to the steel making plant if desired or stored over reasonable periods before use. This stability of the product is a highly important advantage.

While, as I have stated, my steel making process making use of my new carburizing, deoxidizing-degasifying is adapted particularly to the open hearth process it can also be conducted in the electric furnace process. In both cases my impregnated lime can be substituted for all or part of the pig and/ or cast iron conventionally used in these processes. the ladle or even to the mold or wherever a It can also be added to 4 carburizing or deoxidizing action is required in the steel making process.

The following specic examples represent practical operating embodiments of my process wherein steel is made from scrap iron utilizing my new bitumen-impregnated lime product as the sole carburizing, deoxidizing-degasifying substance in the charge.

Example 1 1000 kilos of rock limestone are calcined in such a manner as to obtain a homogeneous product. As soon after the calcination as possible, the product is crushed, sized, dried if necessary and subjected inside an autoclave to a vacuum of about cm. of Hg. during one hour in such a manner as to extract all the occluded gases. 2000 kilos of pitch heated to a temperature of about 250 C. are afterwards injected into the autoclave in which the vacuum has been made. A pressure of 8 kilos per cm.2 is established for about 2 hours, by maintaining the temperature at 250 C. or a temperature near the latter. The excess of pitch is allowed to drain off. In this manner a product containing about 35 per cent by Weight of pitch is obtained.

A product is obtained inside the autoclave which contains the carbon `distributed in the mass of the limestone in a state of division which may be compared to colloidal suspension. The said product is used in the manufacture of steel for the introduction of the non-combined carbon corresponding to the graphitic or combined carbon of the usual cast-iron and of the deoxidizing and degasifying substance.

As an example. the following maybe given:

A charge comprising 50 tons of scrap iron and 2750 kilos of limestone treated as above is charged into an open-hearth furnace. The process of steel manufacture is carried out as usual for an open-hearth operation. A steel is obtained which is very pure and possesses mechanical characteristics which are extremely advantageous. In one operation a steel having the following analysis was obtained: Percent Carbon 0.03

Silicon trace Sulphur 0.010 Phosphorus 0.005 Manganese 0.14 Nickel I 0.05 Chromium 0.35'-

Molybdenum 0.01 Copper 0.01 Tin 0.01 Nitrogen 0.004

. The tensile properties were:

Yield point tons/sq. in. 16.0 Maximum stress 24.5 Elongation percent 48.0 Reduction of area do 84.0 Izod ft. lbs. 81 and 82 The same treatment may of course be carried out in another metallurgical furnace, for instance an electric furnace.

Example 2 Limestone in rock form is calcined so as to make a homogeneous product. The lime obtained is crushed and sized to obtain pieces of uniform size. 1000 kilos of the sized product are introduced into an autoclave and, after heating,

down to their deepest regions.

steel-making charge .into an electric furnace vin l .lieu of thefpigiron conventionally used in-the charge, as a carburizing, deoxidizing-degasifying agent. The heat is conducted as usual and a finished steel is obtained which is exceptionally high grade.

Limestone in rock form is calcined to obtain a uniform product. The product is broken into pieces, sized and the fines eliminated. 1000 kilos of this product are placed in a basket of wire netting. 2000 kilos of pitch are placed in a pot of cast-steel and heated above a naked re surrounded with masonry with a circulation of combustion gases around the pot so as to obtain uniform heating. When the pitch reaches a temperature of about 250 C. the metal basket with its contents is plunged into the pot and the heating is continued for a period of from 3 to 4 hours. The product is then removed from the pot and the excess pitch drained off. Products produced in this manner also contain from about 25 to 35 per cent of pitch by weight depending upon the quality of the limestone and its degree of calcination. This product is used in a steel making process in the same manner as the similar product was used in Example 1.

While I have described what I consider to be the most advantageous embodiments of my process it is obvious, of course, that various modifications can be made in the specific procedures which have been described without departing from the purview of this invention. Thus while I have described impregnation of the lime product at a temperature of about 250 C. it is possible, of course, to obtain substantially the same results over a temperature range extending about 50 to either side of 250 C. The lower temperatures require a somewhat longer period of treatment and are used advantageously with bituminous materials having relatively low melting points. Pitches melting with difficulty may be heated to temperatures somewhat above 250 C. during the impregnating step. In steel making processes making use of my impregnated lime product it may not be necessary to add the conventional slagforming ingredients since my lime product usually performs all of the functions of the usual slag as Well as of the pig or cast iron of the usual charge. Further modifications of my invention which fall within the scope of the following claims will be evident to those skilled in this art.

The impregnation, for certain qualities of bitumen (pitch of high melting point, etc.) may be carried out over a temperature range of from about 250 C. to a temperature 250 C. above the melting point of the bitumen.

What I claim is:

1. In the process of making steel, the improvement which comprises charging a steel furnace with metallic steel-making ingredients and including in said charge substantially as the sole carburizing, deoxidizing-degasifying component "afcarbon-'impregnated Ylime product produl'zfell` by calcining limestone, crushing the yresulting lime, 'treating the resulting lime product in lump form with an excess 'of liquid bituminous .material at temperatures of the Vorder of 250? C. vsubstantially uniformly to impregnate the pores of the lumps with said bituminous material; said bituminous material being solid at ordinary temperaturesand containing hydrocarbons and uncombined carbon;

,andfdraining oif the excess bituminous material to obtain a product in lump form having the structure of the original limestone with from .about 25 to 35 per cent by weight of 'said bitumiin'ou's material` substantially uniformly distributed throughout its pores in a highly dispersed state; and converting the resulting charge in the furnace to produce a carburized steel.

2. The process of claim 1 wherein the said lime product is subjected to a vacuum to remove air from its pores prior to completion of the impregnating step.

3. The process of claim 1 wherein the said lime product is subjected to a vacuum to remove air from its pores and then to superatmospheric pressures to drive said bituminous material into its pores prior to completion of the impregnating step.

4. The process of claim 1 wherein the said lime product is subjected to superatmospheric pressures to drive said molten bituminous material into its pores prior to completion of the impregnating step.

5. The process of claim 1 wherein the said lime product is impregnated by heating it over an open ame with an excess of said bituminous material for a period of from about 3 to 5 hours.

6. In the manufacture of steel, the improvement which comprises charging a steel furnace with metallic steel-making ingredients and including in said charge substantially as the sole carburizing, deoxidizing-degasifying component an impregnated lime product prepared by calcining rock limestone, crushing the resulting lime, promptly applying a high vacuum to the calcined limestone while in lump form to remove occluded gases from its pores, treating the lumps with an excess of a liquid bituminous material at elevated temperatures substantially uniformly to impregnate the pores with bituminous material, said bituminous material being solid at ordinary temperatures and containing hydrocarbons and uncombined carbon, and draining off the excess bituminous material to obtain a product in lump form having the structure of the original limestone with said bituminous material substantially uniformly distributed throughout its pores in a highly dispersed state; and converting the resulting charge in said furnace to produce a carburized steel.

7. The process of claim 6 wherein superatmospheric pressure is applied to the mixture of calcined limestone and bituminous material in said retort to increase the penetration ofthe bituminous material into the pores of the calcined limestone.

' 8. The process of claim 6 wherein the bituminous material is pitch and the impregnating temperature is of the order of 250 C'.

9. In the process of making steel, the improvement which comprises charging a steel furnace with metallic steel-making ingredients and including in said charge substantially as the sole carburizing, deoXidizing-degasifying component a carbon-impregnated lime product produced by calcining limestone, crushing the resulting lime,

treating the resulting lime product in'lump form with an excess of liquid bitumen at temperaturesover a range of from about 250 C. to a temperature 250 C. above the melting point of vthe bitumen substantially uniformly to impregnate the pores of the lumps with said bitumen; said bitumen being solid at ordinary temperatures and containing hydrocarbons and uncombined carbon; and draining off the excess bitumen to obtain a product in lump form having the structure of the original limestone With'from about 25 to 35 per cent by weight of said bitumen substantially uniformly distributed throughout vits pores in a highly dispersed state; and convert- 'in'g the resulting charge in the furnaeeto pralduce a. carburized steel.

JEAN CHARLES FOURMANOIT.

REFERENCES CITED The following references are of record in the `file of this patent:

UNITED STATES PATENTS 

1. IN THE PROCESS OF MAKING STEEL, THE IMPROVEMENT WHICH COMPRISES CHARGING A STEEL FURNACE WITH METALLIC STEEL-MAKING INGREDIENTS AND INCLUDING IN SAID CHARGE SUBSTANTIALLY AS THE SOLE CARBURIZING, DEOXIDIZING-DEGASIFYING COMPONENT A CARBON-IMPREGNATED LIME PRODUCT PRODUCED BY CALCINING LIMESTONE, CRUSHING THE RESULTING LIME, TREATING THE RESULTING LIME PRODUCT IN LUMP FORM WITH AN EXCESS OF LIQUID BITUMINOUS MATERIAL AT TEMPERATURES OF THE ORDER OF 250* C. SUBSTANTIALLY UNIFORMLY TO IMPREGNATE THE PORES OF THE LUMPS WITH SAID BITUMINOUS MATERIAL; SAID BITUMINOUS MATERIAL BEING SOLID AT ORDINARY TEMPERATURES AND CONTAINING HYDROCARBONS AND UNCOMBINED CARBON; AND DRAINING OFF THE EXCESS BITUMINOUS MATERIAL TO OBTAIN A PRODUCT IN LUMP FORM HAVING THE STRUCTURE OF THE ORIGINAL LIMESTONE WITH FORM ABOUT 25 TO 35 PER CENT BY WEIGHT OF SAID BITUMINOUS MATERIAL SUBSTANTIALLY UNIFORMLY DISTRIBUTED THROUGHOUT ITS PORES IN A HIGHLY DISPERSED STATE; AND CONVERTING THE RESULTING CHARGE IN THE FURNACE TO PRODUCE A CARBURIZED STEEL. 